Injection Pressure Fluctuation: Diagnosis Checklist

Injection pressure fluctuation means the pressure response changes between cycles or during the same stage of filling. Pressure is a response signal, not a root cause by itself. It may reflect material feeding, temperature, mold resistance, shot consistency, nozzle contact, or machine movement repeatability.

Quick Answer

Record the pressure pattern before changing pressure settings. A rising trend, sudden spike, low response, or cycle-to-cycle swing each points to a different check. Compare pressure with part weight, visible defects, material feeding, and alarms.

What You May See

• The pressure curve or displayed value changes between cycles.
• Short shots, flash, burn marks, or weight variation appear together with pressure variation.
• Pressure changes after material drying, feeding, colorant, or batch changes.
• Recovery time or screw position does not repeat consistently.
• The controller shows alarms or warnings during injection, recovery, or nozzle movement.

Likely Cause Areas

• Material feeding may be interrupted by bridging, empty hopper, contamination, or inconsistent drying.
• Shot preparation may vary because recovery, screw position, or material density changes.
• Temperature instability may change viscosity and mold resistance.
• Gate, runner, vent, or cavity blockage may make the mold harder to fill.
• Nozzle contact, injection unit movement, or hydraulic or servo behavior may not repeat.
• Insert placement may change flow resistance from cycle to cycle.

Safe Checks Before Adjustment

Stop automatic operation if movement, alarm, guarding, or operator safety is uncertain. Do not place hands in the mold, table, injection, or guarded area while movement is possible. Use photos, controller screenshots, cycle logs, and safe observation before changing several settings.

Diagnosis Path

1. Record pressure values or screenshots for several stable and unstable cycles.
2. Compare pressure changes with part weight, short shot, flash, or burn mark occurrence.
3. Check material feeding continuity, hopper condition, drying, and material batch.
4. Review recovery time, screw position, cushion behavior, and any recovery delay.
5. Check temperature stability at barrel, nozzle, and mold control areas.
6. Inspect whether mold resistance changes because of blocked gate, vent, runner, or insert position.
7. Record any injection unit, hydraulic, or sensor alarm before adjusting settings.
8. Make only one controlled process change after the pressure pattern is documented.

Evidence to Collect

Check	Why It Matters	Evidence to Collect
Pressure trend	Different pressure shapes point to different causes	Controller screenshots or written values by cycle
Part weight and defect record	Links pressure behavior to part output	Weights, defect photos, and cycle count
Feeding condition	Feeding interruptions often cause pressure swings	Hopper, drying, material batch, and recovery notes
Temperature history	Viscosity changes affect mold resistance	Temperature screenshots and alarm history
Machine movement state	Injection unit or sensor issues can change pressure response	Alarm code, movement step, safe video if available

What Not to Change Too Quickly

• Do not correct pressure fluctuation by changing one pressure value without evidence.
• Do not ignore material feeding when pressure and part weight both vary.
• Do not keep running if pressure fluctuation appears with injection unit alarms.
• Do not compare pressure values from different materials or molds without context.

When to Contact Deboge

Contact Deboge when pressure fluctuation appears with alarms, station-specific symptoms, unstable recovery, or repeated part defects. Send pressure screenshots, part photos, weight samples, material records, machine model, and recent changes.

Related Reading

• Process Issues
• troubleshootingmolding defectsshort shot in insert molding
• Controller Settings
• Troubleshooting Center
• Machine Support